Impellers are devices that are widely used in pumping devices, where rotation of the impeller applies pressure to a fluid. Such pumping devices are used in a variety of applications related to pressurization of fluids, including circulation of fluids in closed systems, gas compression, liquid delivery, refrigeration, and propulsion. Both open and closed (i.e., shrouded) impeller designs are known. Closed or shrouded impellers are more difficult to manufacture, however their use is often desired due to their higher efficiency.
A shrouded impeller can be manufactured as an integrated, unitary device or can be assembled from individual components. Integrated, unitary impellers have the advantage of lacking welds, seams, and other manufacturing artifacts that interfere with fluid flow and can be sources of mechanical failure. Manufacture of such unitary shrouded impellers (as disclosed in U.S. Pat. No. 7,3054,762, to Mola) can, however, be an expensive and time consuming process requiring the use of specialized tools capable of reaching deep into the interior of the worked material. Manufacture of a shrouded impeller from individual components is simpler, however joining of the individual parts necessarily introduces the problems of suitably precise alignment of individual components (since even a small misalignment can render a rapidly rotating impeller unstable) and of implementing a suitably consistent and nonintrusive method of joining the components. Such alignment not only needs to ensure that rotating components are concentric, but also that corresponding points of mated components are in spatial alignment.
One approach to aligning the components of a shrouded impeller is to arrange the components in an alignment apparatus or jig prior to joining them, as disclosed in U.S. Pat. No. 3,257,071 (to Harris) and U.S. Pat. No. 4,155,151 (to Stiegelmeier). This approach, however, requires skilled manual adjustment of the components within the jig—a time and resource intensive process that does not lend itself to automation. In addition, aligning the components in such an apparatus does not address the problems associated with joining the aligned components by tacking, welding, or gluing.
Other approaches have attempted to align components of shrouded impellers without the use of a jig or other alignment apparatus. For example, United States Patent Application No. 2011/0,318,183 (to Noronha) describes the assembly of a complex machined component that includes a partially shrouded impeller that has an annular gap in a portion of the shroud cover. The final impeller is assembled using an annular piece dimensioned to fit into the annular gap and held in place by a frictional “snap” interface with the edges of the annular gap. This approach, however, requires complex machining processes and it is not clear how well suited the process is to shrouded impellers of various sizes. In addition, the shroud components are placed directly onto the blades during assembly.
In an alternative approach described in U.S. Pat. No. 8,128,865 (to Jahnz and Freeman), hot isostatic pressing is used to introduce a filler material between the impeller blades of a base piece. The impeller blades and filler are machined to the desired profile and a second hot isostatic pressing process is performed to attach a shroud plate to the impeller blades, after which the filler material is removed by mechanical or chemical processes. This approach still requires careful alignment, however, and the utility is limited by the need to apply considerable mechanical pressure to the relatively delicate impeller blades and by the necessity of complete removal of the filler material.
Another approach, described in U.S. Pat. No. 8,426,766, describes assembling a shrouded impeller by aligning a disc bearing a set of impeller blades with a shroud that has a set of grooves that correspond to the impeller blades. The grooves have a trapezoidal cross section, such that the free edge of an impeller blade is centered within its respective groove when the pieces are brought into contact. The two pieces can then be joined by conventional tacking and welding techniques. This approach, however, leaves a gap between the wide portion of the trapezoidal groove and the sides of the impeller blades, which can act to trap materials and make the impeller difficult to sanitize (for instance, for use in food, dairy, and pharmaceutical processing). It also does not address the problems that can arise from sub-optimal welding processes.
In another approach, described in United States Patent Application No. 2010/0,242,280 (to Adachi et al), a base with multiple resin impeller blades is produced where the impeller blades include protrusions along their free, upper edge. A frustum-shaped shroud plate is brought into contact with these protrusion, and the pieces are pressed together and vibrated to melt and fuse the blade protrusions to the shroud plate. In addition to being limited to plastic or resinous materials that are easily melted, however, this process can introduce flowed resinous material into the spaces between the impeller blades.
All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Thus, there is still a need for robust, scalable, and automatable systems, devices, and methods for producing a multi-part shrouded impeller that provides both concentric and spatial alignment without the need for an external alignment apparatus and that supports a simple and effective joining process.